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Fellow of the Linnean, Geological, and Zoological Societies of London.

Corresponding Member of the Eoyal Academy of Sciences of Berlin ; of the Royal Academy of

Medicine and Philomathic Society of Paris ; and of the Academy of Sciences of

Philadelphia, Moscow, Erlangen, &c.

Professor of Anatomy and Physiology, and Conservator of the Museum of the Royal College of

Surgeons in London.






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Dear Sir,

As the following Observations were made in the course of those pursuits in which you have so warmly- interested yourself, and promoted with the most friendly assistance, I should be wanting in gratitude were I not to address them to you, as a public testimony of the friendship and esteem with which I am,

Dear Sir,

Your obliged and

Very humble Servant,


Leicester Square, Nov. 9, 1786.


To the First Edition of the Animal (Economy, 1786.

The nine following papers have been read at the Royal Society, and published in the Philosophical Transactions ; but in a work of so general a nature, and of which physio- logical inquiries make so small a part, the few facts and observations which I have given upon such subjects may probably be overlooked by those who are not members of that Society. That they may be more easily procured by students in medicine, and other readers, I have, by an ap- plication to the President and Council of the Royal So- ciety, obtained leave to reprint such of them as I consider to be connected with the principles and actions of the Ani- mal GEconomy; and I have added such observations and remarks as have occurred to me since the time they were read before the Royal Society.


To the Second Edition of the Animal (Economy, 1792.

Eleven of the following papers have been read at the Royal Society, and published in the Philosophical Trans- actions ; but in a work of so general a nature, and of which physiological inquiries make so small a part, the few facts and observations which I have given upon such subjects may, probably, be overlooked by those who are not mem- bers of that Society. That they may be more easily pro- cured by students in medicine, and other readers, I have, by an application to the President and Council of the Royal Society, obtained leave to reprint them, in this work, as being connected with the principles and actions of the Animal (Economy; and I have added such observations and remarks as have occurred to me since the time they were read before the Royal Society,


Always an admirer of the genius of Hunter, and of late years obliged by official duties to make frequent reference to his numerous and varied productions, especially to those which are scattered through different volumes of the Philosophical Transactions and other works, I have often felt the inconvenience that resulted from the absence of a uniform edition of the whole of the extant works of that great and original thinker. When, therefore, Mr. Palmer first communicated to me his design of publishing a new edition of Hunter's works, I heard with peculiar satisfaction his intention to include in the proposed collection every memoir of the author that could be found in print, and I gladly lent my assistance, which, however, the previous assiduous researches of Mr. Palmer rendered of little moment, towards completing a list of all the published essays or observations on various parts of the ' Animal (Economy' which had not before been included in the work so entitled. The proposal which Mr. Palmer at the same time made to me to edit this portion of the works of Hunter I declined, from a sense of the inadequacy of my powers to grapple with so vast a range of im-. portant physiological subjects as the contemplated volume must necessarily embrace, and I sincerely hoped that Mr. Palmer would have found a coadjutor better qualified than myself to do justice to this portion of his most useful and praiseworthy undertaking.

After a lapse of nearly two years Mr. Palmer again applied to me to revise the papers on the Animal (Economy, and I then acceded reluctantly to his request, led, by the sole motive of accele- rating the appearance of a much wished-for edition, to a task, to which I have since dedicated a great portion of my leisure hours, without the slightest expectation of profit or honour, the experiment having only served to convince me of the difficulty of adding the observations demanded by the progress of science to the text of Hunter in the spirit of its author, and a retrospect of my annota- tions leading me to suspect that often, with every wish to avoid it, I may have tacitly implied an ignorance on the part of Hunter of facts with which he was probably well acquainted, and to perceive that, in genera], the addition of such details tends to overload and destroy the force of the original observations in the text.

It is with much more satisfaction that I refer to the additions which have been made to the present edition of the Animal (Eco- nomy of the hitherto uncollected or unpublished writings of its original author.


These consist of the following essays.

From the Philosophical Transactions : " On the Anatomy of the Siren or Amphibious Bipes (17C6)." "On the Electric Organs of the Torpedo (1772)." "On the Electric Organs of the Gymnotus (1755)." " Experiments and Observations on Vegetables with respect to the power of producing Heat (1775)."

" A case of Small-pox communicated by the Mother to the Fcetus (1780)."

" Anatomical Remarks on a New Marine Animal (1785)." " Observations on the Structure and (Economy of Whales (1787)."

« On Bees (1792)."

" On the Fibrous Structure of the Crystalline Lens (1793)." " On the Fossil Bones of the Caverns of Gailenreuth (1794)." " Six Croonian Lectures read before the Royal Society by Hunter in the years 1776, 1777, 1779, 1780, 1781, and 1782," but with- drawn from publication by the Author.

From the Medical Commentaries of Dr. William Hunter: " Experiments on Absorption by Veins."

From the Transactions of a Society for the Promotion of Medical and Chirurgical Knowledge, vol. ii. (1794) :

" Description of the Human Uterus and Ovum in the first Month of Pregnancy."

" Observations on the Growth of Bone."

There is also added,

"An Account of the Anatomy of the Jerboa," contributed by Hunter to the Appendix to Russel's History of Aleppo. And, lastly,

" Descriptions of Five Marsupial Quadrupeds," from the Zoo- logical Appendix to White's Voyage to New South Wales. (1790.)

In order to bring these different memoirs in juxtaposition with papers on analogous subjects in the original edition of the Animal GEconomy, a slight alteration has been made in the arrangement of the different essays composing that work. Those which relate to generation are brought together at the beginning of the volume; then follow the observations on digestion, animal heat, and other physiological subjects ; and lastly, the papers of a descriptive character, which refer more immediately to comparative anatomy and zoology. Thus for the first time are collected into one volume the physiological and anatomical stores, from which, in connexion with the materials composing his museum or destined for its illus- tration, an adequate idea may be formed of the nature of the great work in which Hunter had purposed to record the sum of his vast experience.

In the year 1780, when Hunter published a collection of his detached memoirs in the first edition of the Animal CEconomy, he


observes, with reference to the subject of digestion, " I cannot at present spare sufficient time to give my opinions at large on this subject, with all the experiments and observations I have made upon it, but as soon as I have leisure I shall lay them before the public." And again, in describing the organ of hearing in fishes, he premises that he reserves a more complete investigation of this part of natural history " for a larger work on the structure of animals, which I one day hope to have it in my power to publish," and he states that ever since the year 1760 his researches have been continued in every part of the animal ceconomy. Hence instead of regarding the uncommon structures which he discovered in his dissections of different animals as individual peculiarities, he was enabled to advance beyond the anatomists of his own times, and view them from the same eminence to which subsequent induction has raised the observers of the present day : and referring to the series of preparations in his museum, he boldly states with reference to the structure of the organ of hearing in fish, that it is "only a link in the chain of varieties displayed in the formation of this organ of sense in different animals, descending from the most perfect to the most imperfect in a regular progression."

The importance of these views, and the nature and amount of the knowledge which they indicated, could not be appreciated by the contemporaries of Hunter in the absence of a detailed exposi- tion of the evidences on which they were founded. It is no wonder, therefore, that we find his earlier eulogists sometimes founding his claims to scientific eminence on insecure grounds; some, for example, lauding him as the author of a theory of the organizing energy, which may be traced to the time of Aristotle, or as the originator of the doctrine of the vitality of the blood, which is supported with so much eloquence by Harvey and his immediate successors; while others, taking more definite grounds, have often unfortunately selected as his discoveries precisely those subjects of Hunter's special researches in which he had but revived and ex- tended the ideas of his predecessors. Of this we have a striking example in the introductory observations on the character of Hun- ter contained in Sir Everard Home's Lectures on Comparative Anatomy, vol. i., p. 6, in which the independent function of the vesiculas seminales and the determination of the organ of hearing in fishes are adduced as Hunterian discoveries.

The true originators of these and of other ideas and facts which Hunter may have regarded as his discoveries, and which he doubtless did discover so far as independent and original research constitutes a claim to that honour, I have been careful to poim out in every case where my reading has led me to detect in an older author a clear anticipation of Hunter.

It cannot be doubted, however, that the ascription to Hunter by his friends and admirers, of facts and opinions to which he had no title as the original discoverer, must have contributed to lower his character in the estimation of continental anatomists ; whose



acquaintance with the vast accumulation of facts in comparative anatomy due to the labours of the numerous cultivators of that sci- ence in the sixteenth and seventeenth centuries, easily enabled them to detect the weakness of such claims, without perhaps their possess- ing such a knowledge of Hunter's labours as to justly appreciate their scope and tendency, and to view them, as they deserve to be viewed, in the light of a first great attempt to arrange in one con- catenated system the diversified facts in comparative anatomy.

Cuvier, for example, in his review of the progress of science in the latter half of the eighteenth century, a period which may be re- garded as a second revival of comparative anatomy and physiology, places Hunter in an inferior category of contributors to those sciences. After eulogizing the share which the erudite Haller took in demon- strating the importance of comparative anatomy to the advance- ment of physiology, and the corresponding effects which the labours of Daubenton and Pallas produced in establishing sounder ideas of the classification of animals, the historian of the natural sciences goes on to state : " John Hunter in England, the two Monros in Scotland, Camper in Holland, and Vicq D'Azyr in France, were the first who followed their footsteps. Camper," he observes, " cast, so to say, a passing glance of the eye of genius on a number of in- teresting objects, yet almost all his labours were but sketches. Vicq D'Azyr, with more assiduity, was arrested by a premature death in the midst of a brilliant career ; but their works inspired a general interest, which has ever since been on the increase."

With reference to the nature or influence of the labours of Hunter, Cuvier is silent ; he limits himself to an indication in a marginal note of the Treatise on the Teeth and " les autres ecrits de Hunter insares en partiedans les Transactions Philosophiques."*

This was meting out but scanty justice to the author of the Treatise on the Blood and of the Observations on the Animal (Economy, which abound with so many general propositions in comparative anatomy and physiology. If, however, this opinion of Cuvier be excusable under the circumstances under which it was written, it would be unpardonable not to appeal against it upon the evidence of the higher claims of Hunter afforded by the present edition of his works and by those manuscripts which have already appeared in the catalogue of his Physiological collection published by the Royal College of Surgeons. Had these manuscripts, expla- natory of the design of the Hunterian collection, been published before Cuvier wrote the work from which we have just quoted, that astonishing result of Hunter's labours might perhaps have claimed a passing notice from one whose statements all Europe now receives and all posterity will regard with confidence and respect.

" Les autres ecn'ts," the " other writings" of Hunter to which Cuvier alludes, are indeed devoted rather to the development of

* Histoire des Progres des Sciences Naturelles, depuis 1789, torn, i., p. 302


general principles in physiology than to the detail of the anatomical observations upon which he founded them. Many of the facts ascertained in the course of his higher and more comprehensive inquiries, and incidentally alluded to in the narration, are however fully as interesting and important as those which other anatomists have sometimes thought worthy of being made the subjects of express monographs.

But Hunter had higher aims than the reputation of a mere col- lector of facts in comparative anatomy ; and this he not only felt but had expressed in an early period of his career. In a manu- script, copied by Mr. Clift, relating to a dissection of a turtle, he says, " The late Sir John Pringle, knowing of this dissection, often desired me to collect all my dissections of this animal, and send them to the Royal Society ; but the publishing of a description of a single animal, more especially a common one, has never been my wish."

Howsoever we may regret this feeling, which has undoubtedly deprived the world of the results of much inestimable labour, and has operated in various ways disadvantageously to Hunter's own reputation, yet it indicates the expanded views of the man who en- tertained it.

Had Hunter published seriatim his notes of the structures of the animals which he dissected, these contributions to comparative anatomy would not only have vied with the labours of Daubenton as recorded in the Histoire Naturelle of BufFon, or with the Compara- tive Dissections of Vicq d'Azyr which are inserted in the early volumes of the Ency elope1 die Methodique and in the MSmoires de VAcademie Royale de France, but they would have exceeded them both together.

It would be tedious to enumerate, name by name, the different species of animals whose organization was investigated and recorded by Hunter. Mr. Clift has evidence* that he left written descrip- tions, from autopsy, of the anatomy of the following Mammalia:

Of Quadrumana

21 Species.

Carnivora .






Ruminantia .






Marsupiata .


Of Birds .

84 Species.





Of Insects .

29 Species.

Of other invertebrate animals, as mollusca, red-blooded worms, and radiata, upwards of twenty. From the titles of manuscripts, * See " Evidence before the Medical Committee of the House of Commons."


therefore, it appears that Hunter possessed, at the period of his decease, original records of the dissections of three hundred and fifteen different species of animals.

In addition to these, Hunter's preparations testify that he had dissected twenty-three species of mammalia, sixteen species of birds, fourteen species of reptiles, forty species of fishes, forty -two different mollusca, and about sixty species of articulate and radiate animals; all species of animals of whose anatomy we have no evidence that he left written descriptions. So that by adding these undescribed dissections to those of which we derive the evidence from the list of the manuscripts, and of which described dissections his anatomi- cal collection in like manner contains evidences in the dissected and preserved organs, there is proof that Hunter anatomized at least five hundred different species of animals, exclusive of repeated dissections of different individuals of the same species, besides the dissections of plants to a considerable amount.

With respect to the rarer and less known invertebrate animals, Hunter was not content with merely recording their structure and displaying its leading peculiarities in preparations ; but he caused most elaborate and accurate drawings to be made from the recent dissections ; for which purpose he retained in his family many years an accomplished draughtsman, Mr. William Bell, better known as the author of two papers in the Philosophical Transactions, de- scriptive of the Sumatran Rhinoceros and the Ecan Bonna (Platax arthriticus, Cuv.). Several examples of these beautiful designs have already been published by the Council of the Royal College of Sur- geons in the illustrated catalogue of the Hunterian Museum : they relate to the anatomy of the Sepia and Solen, of the Ascidia and Salpa; they illustrate the circulation of the blood in the Crustacea and Anellida ; and the figure which Mr. Hunter has given of the circulation in the Chloeia capillata, a red-blooded worm, far sur- passes in beauty and detail any of those with which Cuvier illus- trates the memoir* dedicated to what he regarded to his latest breath as one of his most interesting discoveries.

Hunter had also minutely investigated the anatomy of the cir- ripedsrf but of his dissections of these, as of many other animals, it is to be lamented that the preparations and drawings are now the sole evidences. The illustrations of the anatomy of the Echinoder- mata, both of the spiny species and of the unarmed Holothuria, have never been surpassed either as to minuteness or accuracy ; and, excepting the disputed article of the nervous system, little is added in the elaborate and well-known monograph of Tiedemann, to the anatomy of the Holothuria as it is displayed by Hunter.J

Now the anatomical labours of Daubenton were confined to that class of animals whose structure most nearly resembles man ; he

* Bulletin de la Soc. Philomath., 1791, p. 146.

f See Physiological Catalogue of the Hunterian Collection, vol. i., p, 255,

pi. IV.

± Ibid., p. 251, pi. HI.


describes the position and length and breadth and number of parts with most praiseworthy zoological precision, but never appears to raise his thoughts to the relations of the structures he detected with the habits of the species, or their adaptation to function. Hence he has been said to have made more discoveries of which he was unconscious than any other cultivator of comparative anatomy.

Vicq d'Azyr, on the contrary, adorns his descriptions with many beautiful and philosophical views, but he did not carry his scalpel beyond the vertebrate series; while Hunter explored every modi- fication of animal structure, from man down to the polype.

If Hunter surpassed his contemporaries in the value and amount of the materials which he collected in comparative anatomy, he rises far above them in the application of his facts.

By a profound and unremitting meditation on the diversities of structure presented to his view, he derived more accurate notions than were current amongst his contemporaries of the parts essen- tial to the performance of the different functions, and every idea or doubt thus suggested he tested by the most varied, ingenious, and accurate experiments.

"Many things," he observes, " arise out of investigation which were not at first conceived ; and even misfortunes in experiments have brought things to our knowledge that were not, and probably could not have been, previously conceived. On the other hand, I have often devised experiments by the fireside or in my carriage, and have also conceived the result ; but when I tried the experi- ment the result was different, or I found the experiment could not be attended with all the circumstances that were suggested."* Few physiologists indeed, if any, have made more numerous, va- rious and conclusive experiments than Hunter. Yet he says, " I think it ma^ ^e set down as an axiom that experiments should not be often repeated which merely tend to establish a principle already known and admitted, but that the next step should be the applica- tion of that principle to useful purposes.''!

By this series of labours of mind and hand, prosecuted uninter- ruptedly from year to year, Hunter at length came to establish a body of physiological doctrines, to the happy influence of which on the treatment of the various " ills that flesh is heir to," every cultivator of the healing science now bears grateful testimony.

Most of the enlightened physiologists of this country have ac- knowledged the high merit and beneficial influence of Hunter's labours; but the general terms in which his merits have been ex- pressed have not availed in raising him from the secondary cate- gory of contributors to comparative anatomy, in which he has been classed by Cuvier, and from which some continental writers have lately been disposed to degrade him.J

* Animal (Economy, p. 417 (the pages throughout refer to the present edition), f Ibid., p. 117.

^ See the Esquisse Historique sur PJlnalomie Comparee, prefixed to the French translation of the second edition of Carus's Comparative Anatomy, vol. i.f p. xxx.


The present seems, therefore, to be a fitting opportunity to attempt to define the grounds for assigning a higher station to Hunter, considered as a physiologist and comparative anatomist. In this endeavour, however, to prove what Hunter was as a dis- coverer, we must also fairly state what he was not.

He has been spoken of as the originator of the idea of a subtle imponderable principle operating in the fluids and solids of the organism, and causing the pheenomena of life. But such a prin- ciple, under various names and with various attributes, has been assigned as the cause of organization by Aristotle, Harvey, Willis, Cudworth, Grew, Van Helmont, and Stahl.

As both Harvey and Hunter had spent laborious lives in earnest inquiries and repeated dissections and experiments, to ascertain relations between structure and function ; as both had studied the changes which take place in the form and structure of animals from their embryo state to that of maturity ; and as both had care- fully traced the successive phsenomena which occur in the egg during incubation, the similarity of their opinions on the nature and powers of the vital principle is correspondingly close.

Both arrived at the conclusion, that an animating principle exists and operates in the ovum prior to the formation of any organ of the future animal. Both attributed the power by which the fecund egg resists putrefaction, while the unprolific one decomposes, to a principle of life, which Harvey more precisely terms the " anima vegetiva"*

Hunter, however, carries his researches a step further ; he sub- mits the fecund egg to a low temperature, and ascertains a new property, of which Harvey was ignorant, a power, viz., of resist- ing cold : he also shows that when once frozen, and killed by cold, the dead impregnated egg yields to putrefaction like the unimpreg- nated one.

Both physiologists observed that if the phasnomena of a vital principle were manifested in one part of the organization more than in another, it was in the blood. "For the blood," says Harvey, "is the first formed, and is the primary animate particle of the em- bryo; it is generated prior to the punctum sal/ens, before the first rudiment of the heart, and is endowed with the vital heat or princi- ple before it begins to move, and from it does pulsation commence.

*"Plurimum itaque mecum ipse repntavi, qui fieret, ut ova improlificaga!- linae supposita, ab eodem calore extraneo corrumpantur, putrescant, et fcetida evadant ; ovis atilem foecundis idem non contingat." Harveii De Generatione Ardmalium Exercitatio 22.

"Ovum itaque est corpus naturale virtute animali preeditum ; principio nempe motus, transmutationis, quietis, et oonservationis." Exercit. 26.

" Cum enim in ovo macula prius dilatetur, cblliquamenlum concoquatur et preeparetur, plurimaque alia (non sine providentia) ad pulli formationem et in- crementum instituanlur, antpqnam quidpiam pulli vel ipsa primogenita ejus particula appareat; quidni utique c.redamus calorem innatum animamque pulli vegetalivam ante pullum ipsum exsistcre V Exercit, 57.


For the thing containing is made to be serviceable to the thing con- tained.

"Nor is the blood therefore to be call the primogcnial part, be- cause that in and from it the organ of pulsation is derived, but also because the animal heat and vital principle are first implanted therein; and in it does life consist. For where heat and motion first begin, there also life doth first arise and last expire. " Harvey, On Generation, pp. 274, 275.

This explicit and beautiful enunciation of the preexistence of the blood to the machine by which it is mainly circulated, and of its endowment of life, fell barren from the pen of Harvey (if we except the brief practice of transfusion to which it gave rise), and was for- gotten, when Hunter resumed the inquiry. And why, it may be asked, was the doctrine of the vitality of the blood inoperative, as taught by Harvey? Because instead of establishing that doctrine by observations and experiments, from which alone it was suscep- tible of deriving further proof, instead of applying the principle to the explanation of the phaenomena of disease, and to a modification and improvement of remedial measures, Harvey obscures and for- gets the conclusion of his cooler moments of observation, and, as the learned Barclay well observes, excited by the discovery which had extended his fame so widely over Europe, and had reflected such lustre on his name and country, he expatiates on the blood as something divine ; he has recourse to hyperbole, and describes its properties in the extravagant language of romance.

Hunter, on the contrary, carries a series of calm and philosophi- cal investigations on the vital properties of the blood to an extent which has never been surpassed ; he examines it under every con- dition, both in the vessels and out of the vessels, during circulation and at rest, in health and in disease. He aims to establish the period in its formation at which it manifests the vital properties ; and he fully details the changes which it undergoes, and the phaeno- mena which supervene in the rest of the organism when these pro- perties are lost. Lastly, he tells us how the blood, by means of its vital properties, assists in the restoration of parts when injured or diseased.

Hunter subjects the blood to both mechanical and chemical analy- sis, and endeavours to determine the characteristic properties of its dif- ferent constituents. It was not known in his time upon which of these constituents the act of coagulation depended. Hunter took advantage of a case in which the red globules subsided, as in some cases they do, more rapidly than usual, and skimming off the super- incumbent colourless fluid, found that the fibrin, as it is now termed, immediately coagulated and formed a colourless clot.* A subse- quent erroneous theory, which attributed the act of coagulation to the red globules, has recently been set aside by the application of an ingenious process for artificially separating the fibrin from the

* Treatise on the Blood, &c, p. 32.


blood disks before coagulation takes place, and the opinions of Hunter on this point have been fully established by the experiments of Miiller. With respect to the serum, Hunter instituted a number of experiments and made many ingenious observations to determine the relative quantity of the coagulable to the uncoagulable part. His deductions as to the amount of nutrient albumen in the blood of animals of different ages, and under different circumstances, as re- gards exercise or rest, &c, formed, from observing the quantity of gravy or uncoagulable serosity which different roasted meats afforded, is highly characteristic of his original and ever active mind. In seek- ing to determine the respective importance of the different constitu- ents of the blood, by the philosophical and most difficult inquiry into their respective periods of formation in the development of the embryo, Hunter made the interesting discovery that the vessels of the embryo of a red-blooded animal circulated in the first instance colourless blood, as in the invertebrate animals.

" The red globules," he observes, " seem to be formed later in life than the other two constituents, for we see while the chick is in the egg the heart beating, and it then contains a transparent fluid before any red globules are formed, which fluid we may suppose to be the serum and the lymph."*

I well remember the feelings of surprise with which I listened while at Paris in 1832 to a memoir read before the Academy of Sciences by MM. Delpech and Coste, the object of which was the announcement of the same fact as a novel and important discovery. The statement of the French observers was received with all the consideration which its importance justly merited, without its being suspected that our great physiologist had half a century before em- braced it, with all its legitimate deduction, in the extended circle of his investigations.

In the same spirit in which he investigated the nature of the blood he also pursued his researches on the properties of the solids; he endeavours to determine the specific powers and vital phaenomena of the nervous system and of the stomach ; he compares these im- portant parts of the animal body, with reference to the degree of energy with which their functions are manifested ; he considers the influence which they reciprocally exert in maintaining the vitality of the blood, and the relative dependence of the whole organism on the integrity of their vital powers. He also dwells at great length on the sympathies resulting from these mutual relations and de- pendencies.

In all his physiological researches we may see that instead of dogmatising on the powers and virtues of an abstract essence, Hunter endeavours to analyse the vital forces peculiar to each organic element, and to classify, as it were, the phaenomena of which life consists.

If we turn from Hunter's researches on life to his investigations

* Treatise on the Blood, &c, p. 71.


on another equally difficult and recondite subject in general physio- logy, viz., Animal, or rather, Organic Heat, we see the same exer- cise of the powers of the same great and original mind.

He first determines the relative extent to which the power of generating heat or resisting cold is enjoyed in the two grand divi- sions of organic nature, plants and animals : he next investigates the degree in which that power is possessed by different classes of animals; then the relation subsisting between that degree and the perfection and complexity of the organization with which the power is associated. He anticipates some modern physiologists in determin- ing the different power of generating heat manifested by the same species at different periods of life, and advances a step further by considering the different powers of resisting cold which different parts of the same organized body possess in relation to their re- spective ages and periods of formation.* He lastly analyses, so to say, the different functions, to determine in what degree the pro- duction of heat depends on their exercise; and reciprocally, the in- fluence of the temperature of the body upon the active and healthy maintenance of their function.

Throughout all this beautiful and justly celebrated inquiry we sec the philosopher conscious of the extent of his powers, and of the kind of knowledge which the right exercise of those powers was adapted to acquire. We now here perceive a trace of a desire to establish a theory of the nature of animal heat in the abstract.

Let any one compare the language of Harvey or of Willis, while expatiating on the caliduminnatum, with the following just remark: " I shall not," says Hunter, " attempt to settle whether heat, is a body or matter, or only a property of matter, which appears to me to be merely a difference in terms, for a property must belong to something."!

It is precisely in the same spirit that he conducts his researches on life ; and I would say, after a very careful study of the writings of Hunter, that of all physiologists he is one to whom a dogmatic theory of abstract life can least be attributed. But by those whose notions of Hunter's doctrines are founded solely on a perusal of the posthumous " Treatise on the Blood" he is liable to be misconceived, and in opinions expressed from that limited acquaintance with his writings to be misrepresented.

With the just ideas which Hunter had acquired of the laws of vitality and organic heat he was enabled to explain many of the phasnomena of digestion more satisfactorily than had been done by his predecessors Spallanzani and Reaumur.

The following is a fair example of the different views and Kinds of knowledge which these experiments brought to the inquiry.

Spallanzani had observed that digestion did not go on in rep- tiles below a certain temperature, he thought therefore that heat

* P. 158. f P. 162.


was necessary to assist in the dissolving processes of the sto- mach ; Hunter, referring to the same fact, shows that the influence here is not merely chemical, but that the heat operates by first raising the sensitive powers, these then transmit the stimulus to the respiratory and circulating functions, and lastlylto the motive and other actions and faculties, and that the digestive organs are necessarily excited to corresponding actions, in order to supply the waste occasioned by the working of the machine, which the heat has thus called into play.

Hunter more accurately determined, and first applied and render- ed fruitful the fact which Grew incidentally mentions, viz., That it is the property of a living body or part to resist the action of the gastric juice ; and his celebrated paper " On the Digestion of the Stomach after Death," is a beautiful example of the application of his general view in physiology to the explanation of particular phenomena.

Of all his published writing, the paper on Digestion convey perhaps the best idea of the extent of Hunter's researches in Com- parative Anatomy, and of the soundness of his reasonings in General Physiology.

Hunter's claims to the originality of observations which have been reproduced as new by late physiologists, I have pointed out in the notes to these and other memoirs ; and have particularly endea- voured to define the merit of Hunter as a discoverer in reference to the absorbent system.

Hunter's published writings on the Nervous System bear but a small proportion to the extent of his anatomical investigations on this subject, especially as they are manifested in the philosophical series of preparations in the Gallery of his collection, in which the nervous system is traced through its progressive stages of compli- cation, from the simple filaments of the entozoon and echinoderm, to the aggregated masses which distinguish the organization of man. The fibrous structure of the brain, the discovery of which, though due to Goiter as early as 1573, has sometimes been attributed to Reil and Gall, is displayed by Hunter in preparations made to show the fact (Nos. 1335, 1336), and is expressly mentioned in the description of the Anatomy of the Whale Tribe.*

In treating of the comparative anatomy of the nervous system in his introductory observations to this division of his Collection^ Hunter rises to the following generalizations. He divides the ani- mals which have brains, or visible aggregations of the nervous sub- stance, into six classes, each characterized by a peculiar modifi- cation of the brain.

The first class'' has a brain in the form of a ring, through which passes the oesophagus, and from which the nerves arise, like radii from a centre. It consists of a pulpy substance, somewhat trans- parent, which is easily squeezed out when the brain is cut into. It

* P. 373. f Physiological Catalogue, vol. iii., p. 4.


is not enclosed in hard parts, and is not defended from pressure or injuries more than any other internal part.

The examples of this type in his Museum are selected from the gastropodous class of Mollusca. The same condition of the nervous system we now know, from the i*esearches of Cuvier, to charac- terize the whole of a vast division of invertebrate animals, including, amongst the highest organized of that division, certain species, the dibranchiate Cephalopods, in which the character, as expressed by Hunter, is affected by the development of a cartilaginous cranium for the protection of the cerebral ring ; but ulterior researches have not led to any modification of Hunter's description of the typical form of the brain in the Molluscous sub-kingdom.

In the 'second class ' the brain lies in the head of the animals ; it is a pulpy substance, somewhat transparent, which gives it a bluish cast; from its lower part go out two large nerves, one passes on each side of the oesophagus, and ihey then unite into one, form- ing a knot at their union ; they disunite again, and so unite and disunite alternately through the whole length of the animal, at every union giving off the nerves as from the brain. This structure, Hunter says, he suspects to answer both the use of a medulla spinalis and the great intercostal nerve.

The examples of the class of animals adduced by Hunter as being characterized by this essential form of the nervous system are the leech, earthworm, aphrodita, centipede, caterpillar, scorpion, and lobster. Subsequent researches have shown that it exists in the barnacles, or Cirripedia, which most zoologists now rank in the same primary division with the Anellides, Insects, Arachnidans, and Crustaceans.

In the first class of animals in this neurological arrangement (for in enunciating general propositions respecting any given organ the comparative anatomist becomes involuntarily, as it were, a classi- ficator of animals as well as organs), Hunter observes, " we had the brain surrounded by soft parts only. In the second it was closely surrounded by soft parts, but these were surrounded by hard. In the < third class' the brain has a case of hard parts for itself, called the skull."

Now when Hunter made a brain relatively larger than in his first two classes protected by a skull, and continuous with a medulla spinalis extended down the back, and an endowment of the five senses, the essential neurological characters of his third class of animals. he erred in not applying them to his fourth, fifth, and sixth classes, as an attribute common to all, and one which dis- tinguished each alike from the two lower classes. The apprecia- tion of the great natural group characterized by a brain and spinal chord, situated on the dorsal aspect of the body, and protected by a vertebral case, was reserved for the sagacious penetration of Cuvier.

However, in so far as Hunter limits his generalizations to the brain alone, he is consistent with himself, and exact in the differential


characters which he points out. The brain in fish, for example, or his « third class? is a very irregular mass, inconstant in its form and in the number of its parts ; still the " several parts which are similar to those in a superior class may be picked out;" the skull, more- over, is too large for the brain, and the interspace is filled by a cellular membrane, which Hunter compares to the arachnoid.

In the 'fourth class,' the parts composing the brain " do not lie one upon another, but are very much detached and follow one another," in short, are characterized by their linear arrangement ; a character, the accuracy of which, as applied to the Reptilia, has been confirmed by all subsequent experience. It is interesting to observe how Hunter determines the nature of these different de- tached masses. He says, " The two anterior consist of the cere- brum ; the two middle, I should suppose, of the nates and testes, which I take to be the middle lobes detached, because in the bird they are more underneath, not so much between the cerebrum and cerebellum ; the posterior is the cerebellum, consisting of one body entirely."* Every eminence, Hunter further observes, has a cavity or ventricle in it. The linear arrangement of the masses of the brain is common both to fishes and reptiles; but the relation of those masses to the skull, and their variable number and propor- tions, according to Hunter, distinguish the brain in fish. He further observes that in the crocodile the parts of the brain are more closely connected, and that the skull is more in contact with it, in which respect it comes nearer the bird than do any of the other amphibia.

The brain in the 'fifth class,' or fowl, Hunter characterizes by its greater relative size, and the superposition of its component masses.

In the ' sixth class,' or quadrupeds, the brain is in general larger than in the preceding, and the parts more compacted, the whole mass being brought into nearly a globular figure. " The nates and testes are four small bodies, with no visible cavities; are not